There is known a wafer for semiconductor devices, which includes an oxide film, e.g., a TEOS (Tetra Ethyl Ortho Silicate) film, which contains impurities formed on a silicon base by a CVD process or the like; a conductive film, such as a TiN film; an antireflection film (BARC film); and a mask layer (photoresist film) that are stacked one on top of another (see, e.g., Japanese Patent Application Publication No. 2006-190939). The photoresist film is formed to have a predetermined pattern by photolithography, and serves as a mask layer upon etching the antireflection film and the conductive film.
Recently, semiconductor devices are becoming smaller and smaller, and it is required to form a circuit pattern on the surface of the wafer more finely. To form such a fine circuit pattern, it is needed to make the minimum dimension of pattern in the photoresist film small in the fabrication of the semiconductor devices so that an opening (via hole or trench) with a small dimension may be formed in an etching target film.
The minimum dimension of pattern in the photoresist film is defined depending on the minimum dimension that may be developed in photolithography, however, the minimum dimension that may be accomplished by photolithography in a mass-production has a limitation due to a deviation in a focal length. For example, the minimum dimension achievable is about 80 nm. Meanwhile, a processing dimension that satisfies the requirement of scaling-down for miniaturization of semiconductor devices is about 30 nm.
Further, photoresist films smoother and thinner than those of the prior art have been widely applied and the wavelength of light used for photolithography has been shortened in order to reduce the minimum dimension of the pattern. This causes a problem that the photoresist film itself is worn when the antireflection film (BARC film) is etched. Thus, it has been accelerated to develop a technology to increase or recover the thickness of the photoresist film.